Carbon fibers are widely used as reinforcements in composite material structural products. Most typically carbon fibers are combined with polymeric matrix materials through a variety of manufacturing processes and molded into structural parts used in a wide variety of applications, including airplanes, sporting goods, boats, automobiles and numerous other consumer and industrial products.
Often the carbon fibers are used to produce intermediate products such as prepregs, fabrics, molding compounds, and other product forms supplied to molders for further processing into structural components. Each of these intermediate product forms has application limitations with positive and negative attributes, with added cost to supply chain being the most negative.
Further, carbon fibers are typically produced as very large filament count tows, typically 3,000 to over 50,000 carbon filaments in a tow bundle. The carbon filaments have a diameter of approximately 7.2 microns (10−6 millimeter) or less. The fibers and tows may be, for example, manufactured as described in U.S. Pat. No. 6,385,828 of Kiss, et al., which is incorporated herein by reference. This combination of large filament count and small filament diameter gives a very high total surface area within the carbon fiber tow which makes fully wetting these filaments with a polymeric matrix material very difficult. This complete wetting of the filaments facilitates achieving good structural properties in the composite material.
In addition, the molding step requires that this matrix flows to fill the mold cavity, and the rate at which this flow takes place is an important factor in the efficiency of the molding process, along with the resulting product.
When the fibers become longer (e.g., over 1 inch) and/or a larger number of fiber filaments group together, it becomes increasingly difficult to disperse the fibers, creating very real processing issues. In particular, the failure to uniformly disperse such filaments inhibits the flow properties of the product, which can lead to the creation of void spaces and other anomalies in the final product.